The invention is directed to a battery pack for hand-held electric machine tools.
Battery packs, particularly for hand-held electric machine tools with high power requirements such as drill hammers and hand-held circular saws, must be able to be recharged quickly to enable quasi-continuous use of the hand-held electric machine tool by exchanging another battery pack. Battery-specific limiting values, particularly temperature, must be taken into account when charging and discharging to achieve a sufficiently long life of the battery pack. For this purpose, the temperature of the battery pack is commonly monitored by a standardized analog temperature sensor, which is arranged in the battery pack and is constructed as a temperature-dependent resistor with a negative temperature coefficient. When a limiting value is exceeded, the current flow is interrupted by battery protection electronics with a power switch, such as a power MOSFET, arranged in the circuit path.
NiCd and NiMH battery packs for hand-held electric machine tools which are interchangeable from one manufacturer to another by standardized interfaces to the consumer or the charging device are well represented commercially. These NiCd and NiMH battery packs have a standardized analog temperature sensor, which is arranged in the battery pack and is constructed as a temperature-dependent resistor with a negative temperature coefficient. However, the protective function aimed at protecting the battery is achieved only when the battery protection electronics of the consumer and charging device are used and set correctly. Problems occur particularly due to the fact that the battery cells, e.g., NiCD cells, NiMH cells or the especially sensitive Li-ion cells, have identical geometric constructions but must be used differently with respect to the limiting values.
It is also known to arrange the battery protection electronics in their entirety in the battery pack. The high currents required in battery packs for hand-held electric machine tools generate considerable amounts of heat due to the internal resistance of the power switch, which increases temperatures. Reducing the internal resistance of the power switch through the use of special low-impedance power MOSFETs or a plurality of power MOSFETs connected in parallel, as is commonly done, is uneconomical particularly in view of the high piece numbers of battery packs, since a large quantity of battery packs is used for every hand-held electric machine tool during its useful life.
According to NL9201744, a hand-held electric machine tool that is powered by a battery pack has battery protection electronics. An analog temperature sensor is arranged in the battery and a battery protection logic and power switch arranged in the hand-held electric machine tool can be used to control the motor and act as a charging device. The battery has an externally accessible temperature measuring interface to the battery protection logic for measuring the battery temperature.
According to EP0448767, a battery pack for diverse consumers and a charging device connected thereto form modular battery protection electronics. A temperature sensor and the battery protection logic are arranged in the battery pack. The battery protection logic controls a power switch arranged in the charging device by digital serial control pulses of an electronic control interface. The digital control can be decoded only by the charging devices or consumers specifically associated with the battery and therefore can only function with these specific charging devices and consumers.